Recyclable and reusable PdCl2(PPh3)2/PEG-400/H2O system for the hydrophenylation of alkynes with sodium tetraphenylborate

Article abstract of DOI:10.1177/1747519820934379

A stable and efficient PdCl₂(PPh₃)₂/PEG-400/H₂O catalytic system for the hydrophenylation reaction of alkynes has been developed. In the presence of 3 mol% PdCl₂(PPh₃)₂ and 2 equiv. of HOAc, the hydrophenylation of both terminal and internal alkynes with sodium tetraphenylborate proceeded smoothly in a mixture of PEG-400 and water at room temperature or 50 °C to afford a variety of phenyl-substituted alkenes in moderate to high yields. The isolation of the products was easily performed by extraction with petroleum ether, and the PdCl₂(PPh₃)₂/PEG-400/H₂O system could be readily recycled and reused six times without apparent loss of catalytic activity.

Full text of DOI:10.1177/1747519820934379

934379CHL0010.1177/1747519820934379Journal of Chemical ResearchLiu et al.
research-article2020
Research Paper
Journal of Chemical Research
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Recyclable and reusable PdCl2(PPh3)2/PEG-400/
H2O system for the hydrophenylation of alkynes
with sodium tetraphenylborate
https://doi.org/10.1177/1747519820934379
DOI: 10.1177/1747519820934379
journals.sagepub.com/home/chl
Rong Liu, Tingli Zhang, Bin Huang and Mingzhong Cai
Abstract
A stable and efficient PdCl2(PPh3)2/PEG-400/H2O catalytic system for the hydrophenylation reaction of alkynes has
been developed. In the presence of 3mol% PdCl2(PPh3)2 and 2 equiv. of HOAc, the hydrophenylation of both terminal
and internal alkynes with sodium tetraphenylborate proceeded smoothly in a mixture of PEG-400 and water at room
temperature or 50°C to afford a variety of phenyl-substituted alkenes in moderate to high yields. The isolation of the
products was easily performed by extraction with petroleum ether, and the PdCl2(PPh3)2/PEG-400/H2O system could
be readily recycled and reused six times without apparent loss of catalytic activity.
Keywords
alkyne, green chemistry, hydrophenylation, palladium, PEG-400
Date received: 7 April 2020; accepted: 23 May 2020
H
R
PdCl2(PPh3)2 (3 mol%)
HOAc(2.0 equiv)
R
Ph
R
H
+
NaBPh4
R1
R1
Ph
R
PEG-400 H O (1:1)
/
2
R
R1 (1.0 or 0.33 equiv)
r.t. or 50oC
+
Ph
H
H
Recyclable catalytic system!
providing a mixture of alkene derivatives.20–23 Recently,
the employment of arylboron compounds in hydroaryla-
tion reactions drew considerable attention because of their
ready availability, stability, and high functional group
compatibility.24–28 Hayashi et al.29 reported hydroarylation
of alkynes with arylboronic acids, and the reaction has
been expanded to the arylative cyclization of aldehydes
and alkyne-tethered alkenes.30,31 Sodium tetraphenylborate
is a stable and inexpensive phenylating reagent and has
been widely used in organic synthesis. Palladium-catalyzed
hydrophenylation of alkenes32 and alkynes33 with sodium
tetraphenylborate has been reported to proceed smoothly
under mild conditions. However, the hydrophenylation
Introduction
Styrenes are important structural motifs extensively pre-
sented in pharmaceuticals, natural or synthetic products,
and functional materials.1–5 Traditionally, styrenes are
prepared by the Wittig6 or Peterson olefinations7 and
insertions of alkynes into organometallic reagents,8–10
which are waste-intensive and require prefunctionalized
starting materials. Catalytic methods such as the olefin
metathesis11,12 and Heck coupling reactions13 are more
atom-economic but also employ prefunctionalized arenes
as substrates. In addition, C–H vinylations of the
Fujiwara–Moritani type have provided an efficient route
to styrenes, but stoichiometric oxidants are required.14–16
In recent years, catalytic hydroarylation of alkynes has
attracted considerable interest because it allows for the
atom-economical construction of functionalized alkenes
from relatively simple arenes and alkynes.17–19 The
hydroarylations of alkynes catalyzed by transition metal
complex or Lewis acid through C–H bond activation of
arenes have been widely investigated, but most research
has mainly focused on the electron-rich arenes, and the
Key Laboratory of Functional Small Organic Molecule, Ministry of
Education and Department of Chemistry, Jiangxi Normal University,
Nanchang, P.R. China
Corresponding author:
Mingzhong Cai, Key Laboratory of Functional Small Organic Molecule,
Ministry of Education and Department of Chemistry, Jiangxi Normal
University, Nanchang 330022, P.R. China.
regiocontrol of the reaction is still difficult, thereby Email: caimzhong@163.com

2
Journal of Chemical Research 00(0)
reaction generally proceeds in the presence of a homoge- amount of HOAc or palladium catalyst loading was found to
neouspalladiumcatalystsuchasPd(OAc)2 orPdCl2(PPh3)2, further promote the reaction, and moderate yields were
which makes the recovery of the expensive palladium cat- achieved (Table 1, entries 4–6). Our next studies focused on
alyst tedious if not impossible and might cause unaccepta- the influence of solvent on the model reaction. It was found
ble palladium contamination of the product. Therefore, that a mixture of PEG-400 and water was more effective
from the standpoint of green and sustainable chemistry, the than PEG-400 alone as solvent (Table 1, entries 7–10). The
development of recyclable and reusable palladium cata- reaction performed in PEG-400/H2O (V/V, 1:1) gave the
lytic systems for these important organic transformations desired 2a in 94% yield (Table 1, entry 9). In addition, the
is highly desirable.
efficiency of various chain length PEGs on the model reac-
As green organic synthesis is attracting more and more tion was investigated (Table 1, entries 11 and 12). PEG-400
attention, the use of eco-friendly, green solvents is highly was found to be superior to PEG-600 and PEG-1000. Other
desirable. To address the recyclability of metal catalysts palladium catalysts such as Pd(OAc)2, PdCl2, and Pd(PPh3)4
and environmental concerns, a convenient and efficient were also tested, but none of them exhibited good catalytic
way is to anchor the catalyst in a liquid phase by dissolving activity (Table 1, entries 13–15). Reducing palladium load-
it into a nonvolatile and nonmixing liquid, such as ing from 3 to 1mol% resulted in a significant decrease in the
poly(ethylene glycols) (PEGs)34–36 and ionic liquids.37 yield of 2a (Table 1, entry 16). Thus, the optimal catalytic
Generally, ionic liquids require a complicated preparative system involved the use of PdCl2(PPh3)2 (3mol%), HOAc
procedure, and their environmental safety is still being (2.0 equiv.) in PEG-400/H2O (V/V, 1:1) at room temperature
debated because the toxicity and environmental burden under Ar for 6h (Table 1, entry 9).
data are unknown for most of the ionic liquids. By contrast,
Having achieved satisfactory results in the hydrophe-
PEGs are easily available and cheap, thermally stable, bio- nylation of 1,2-diphenylacetylene with NaBPh4, then, vari-
degradable, recoverable, and nontoxic liquid polymers ous internal and terminal alkynes were examined to explore
which can be used as efficient media for eco-friendly and the scope of substrates under the optimized reaction condi-
safe chemical reactions. Recently, PEGs have been widely tions and the results are listed in Table 2. As expected, sym-
utilized as green solvents for the palladium-catalyzed car- metrical internal alkynes 1b–d displayed a similar reactivity
bon–carbon bond-forming reactions such as the Heck cou- as 1a and the hydrophenylation reactions proceeded
pling,38 the Suzuki coupling,39–41 the homo-coupling and smoothly to give the corresponding trisubstituted phenyl
cross-coupling of aryl halides,42 the direct arylation of alkenes 2b–d in 70%–84% yields. Furthermore, the hydro-
1,2,3-triazoles with aryl bromides,43 the Hiyama coupling,44 phenylation of electron-poor internal alkyne 1e provided
carbonylativeSuzukicoupling,45 carbonylativeSonogashira the adduct 2e in 80% yield. As for unsymmetrical internal
coupling,46 and the homo-coupling of arylboronic acids47 alkynes, the reactions also took place effectively, and the
with easy recyclability of the solvents and Pd catalysts. regioselectivity depends on the nature of substituents. For
However, to the best of our knowledge, no palladium-cata- example, the use of methyl but-2-ynoate 1f or ethyl but-2-
lyzed hydrophenylation reaction of alkenes or alkynes with ynoate 1g led to the formation of methyl 3-phenyl-
sodium tetraphenylborate in PEGs has been described until 2-butenoate 2f or ethyl 3-phenyl-2-butenoate 2g,
now. Herein, we report the application of PdCl2(PPh3)2/ respectively, in excellent yields and regioselectivity, indi-
PEG-400/H2O system as a highly efficient and reusable cating that the phenyl group was almost exclusively added
catalytic medium for the hydrophenylation of alkynes with to the β-carbon of the ynoate due to the presence of the
sodium tetraphenylborate. This affords a variety of phenyl- strongly polarized C–C triple bond. The reaction of ethyl
substituted alkenes in moderate to high yields. The devel- oct-2-ynoate 1h also proceeded smoothly with high yield,
oped methodology shows important practical advantages but a slightly lower regioselectivity of 93% was observed.
deserving special note.
Notably, ethyl 3-phenylpropiolate 1i showed a similar reac-
tivity as 1f and 1g to furnish the expected product 2i in 92%
yield and excellent regioselectivity. But, in the case of
1-phenylpropyne 1j, the two regioisomers 2j and 3j resulted
Results and discussion
In our initial screening experiments, the hydrophenylation from the cis-addition of NaBPh4 to 1j were obtained in 43%
of 1,2-diphenylacetylene (1a) with NaBPh4 was selected as and 32% yields, respectively. To our delight, when terminal
model reaction to optimize the reaction conditions. The alkynes were used as substrates, the hydrophenylation reac-
effects of acids, solvents, and palladium catalysts on the tions also worked well with high regioselectivity in favor of
reaction were studied, and the results are given in Table 1. the Markovnikov adducts. For instance, the hydrophenyla-
At first, the acid effect was examined using PdCl2(PPh3)2 tion reactions of 1-hexyne 1k, 1-octyne 1l, and 5-phenyl-
(1mol%) as catalyst with PEG-400 as solvent at room tem- 1-pentyne 1n afforded the corresponding phenyl-substituted
perature (entries 1–3). It is evident that the reaction pro- alkenes 2k, 2l, and 2n, respectively, in 78%–89% yields.
duced only a trace of target product 2a in the absence of any However, in the cases of phenylacetylene 1m, 5-chloro-
acid additive (Table 1, entry 1), and a low yield of 2a was 1-pentyne 1o, and 5-cyano-1-pentyne 1p, the correspond-
obtained when 1 equiv. of HCl was used as the additive ing adducts 2m, 2o, and 2p were obtained in relatively
(Table 1, entry 2). However, when 1 equiv. of HOAc was lower yields of 48%–60%.
used as the additive, the reaction was improved and afforded
Sodium tetraarylborates are usually prepared by the
the desired 2a in 38% yield (Table 1, entry 3). Increasing the reaction of arylmagnesium bromides with trimethyl

Liu et al.
3
Table 1. Reaction of 1,2-diphenylacetylene (1a) with NaBPh4.a
Ph
H
Ph
Ph
Pd catalyst
+
NaBPh4
Ph
Ph
Acid, solvent, r.t.
1a
2a
Entry
Pd catalyst (mol%)
Solvent (V/V)
Acid (equiv. to 1a)
Yield (%)b
1
2
3
4
5
6
7
8
PdCl2(PPh3)2 (1)
PdCl2(PPh3)2 (1)
PdCl2(PPh3)2 (1)
PdCl2(PPh3)2 (1)
PdCl2(PPh3)2 (2)
PdCl2(PPh3)2 (3)
PdCl2(PPh3)2 (3)
PdCl2(PPh3)2 (3)
PdCl2(PPh3)2 (3)
PdCl2(PPh3)2 (3)
PdCl2(PPh3)2 (3)
PdCl2(PPh3)2 (3)
Pd(OAc)2 (3)
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400
PEG-400/H2O (3:1)
PEG-400/H2O (2:1)
PEG-400/H2O (1:1)
PEG-400/H2O (1:2)
PEG-600/H2O (1:1)
PEG-1000/H2O (1:1)
PEG-400/H2O (1:1)
PEG-400/H2O (1:1)
PEG-400/H2O (1:1)
PEG-400/H2O (1:1)
None
HCl (1.0)
Trace
9
HOAc (1.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
HOAc (2.0)
38
48
58
67
78
86
94
91
87
74
11
15
29
48
9
10
11
12
13
14
15
16
PdCl2 (3)
Pd(PPh3)4 (3)
PdCl2(PPh3)2 (1)
aReactions were carried out with 1a (1.0mmol), NaBPh4 (1.0mmol), palladium catalyst, and acid in solvent (2mL) in a sealed tube at room
temperature under Ar for 6h.
bIsolated yield.
borate, followed by hydrolysis. To explore the scope of internal alkynes with various arylboronic acids also took place
the borates, we prepared sodium tetrakis(4-methylphenyl) smoothly at room temperature in PEG-400/H2O (1:1) to give
borate via a complicated procedure starting from 4-bro- the corresponding trisubstituted aryl alkenes in moderate
motoluene, magnesium turnings, and trimethyl borate. yields. We next carried out the reaction of 1,2-diphenylacety-
The reaction of ethyl but-2-ynoate 1g with sodium lene 1a with PhB(OH)2 under the conditions shown in Scheme
tetrakis(4-methylphenyl)borate also proceeded smoothly 1 for direct comparison to the sodium tetraphenylborate, but
under the conditions presented in Table 2 to afford the the desired 2a was isolated in only 55% yield.
desired (E)-ethyl 3-p-tolylbut-2-enoate 4b in 88% yield
with regioselectivity of 99%.
A possible mechanism for the palladium-catalyzed
hydrophenylation of alkynes with NaBPh4 is illustrated in
To explore the possibility for further efficient transfer of Scheme 2. First, oxidative addition of the C–B bond of
phenyl groups in NaBPh4, we examined the reaction of 1a Ph3B formed in situ from reaction of NaBPh4 with HOAc to
with 0.33 equiv. of NaBPh4 in PEG-400/H2O (1:1) under (Ph3P)2Pd(0) produces intermediate A.32 Subsequent selec-
different conditions. It was found that when the reaction tive insertion of the alkyne 1 into the Pd–C bond gives
was carried out at 50°C for 12h, the desired product 2a was intermediate B, which undergoes a hydrolysis reaction to
produced in 91% yield, indicating that at most three phenyl provide intermediate C. Finally, reductive elimination of
groups in NaBPh4 could be efficiently utilized. We next intermediate C affords the desired phenyl-substituted alk-
performed the reaction of 0.33 equiv. of NaBPh4 with sev- ene 2 and regenerates (Ph3P)2Pd(0) to complete the cata-
eral other alkynes at 50°C in PEG-400/H2O (1:1), and the lytic cycle. In addition to Ph3B, Ph2BOH and PhB(OH)2
results are given in Table 3. As shown in Table 3, both sym- could also be possible intermediates in the palladium-cata-
metrical and unsymmetrical internal alkynes underwent the lyzed hydrophenylation reaction of alkynes with NaBPh4.
hydrophenylation reaction smoothly to afford the corre-
To evaluate the reusability of the solvent and the catalyst,
sponding adducts in good to high yields. But, the reactions the hydrophenylation reaction of 1,2-diphenylacetylene
of terminal alkynes 1l–n with 0.33 equiv. of NaBPh4 gave (1mmol) with NaBPh4 (1mmol) was investigated in the
the desired products 2l–n in only 39%–54% yields.
presence of PdCl2(PPh3)2 (3mol%) and HOAc (2.0 equiv.)
It was reported that the reaction of NaBPh4 with HOAc in PEG-400/H2O (V/V=1:1, 2mL) at room temperature. As
could produce Ph3B, benzene, and NaOAc, and Ph3B could shown in Table 4, we were pleased to observe that the
react with H2O further to form di- and monophenylboronic PdCl2(PPh3)2/PEG-400/H2O system could be recycled and
acid.32 Thus, we also studied the reactivity of arylboronic acids reused up to six times without apparent loss of catalytic
with alkynes at room temperature (Scheme 1). As shown in activity. After initial experimentation, the reaction mixture
Scheme 1, the palladium-catalyzed hydroarylation reaction of was extracted with petroleum ether (3×10mL), and the

4
Journal of Chemical Research 00(0)
Table 2. PdCl2(PPh3)2-catalyzed hydrophenylation reaction of alkynes with NaBPh4 in PEG-400/H2O.a,b
PdCl2(PPh3)2
(3 mol%)
R1
R1
Ph
R
R
H
R1
+
NaBPh4
+
R
PEG-400/H2O (1:1)
(1.0 equiv)
Ph
H
1
HOAc (2.0 equiv), r.t., 6 h
2
3
n-Bu
n-Pr
n-Bu
n-Pr
Et
H
Ph
t
E
Ph
Ph
CO2Me
MeO2C
Ph
Ph
2b
H
, 94%
Ph
2c
Ph
2d
H
, 82%
H
, 84%
H
2a
2e
, 80%
, 70%
Me
CO2Me
H
Me
n-C5H11
CO2Et
Et
CO2
CO2Et
Ph
Ph
Ph
Ph
2g
H
Ph
H
H
2f
2:3c
2:3c
2h
2:3c
2i
, 92%;
2:3c
, 94%;
> 99
, 91%;
> 99
, 85%;
= 93:7
> 99
n-C6H13
H
Me
Ph
Me
Ph
n-Bu
H
H
Ph
H
Ph
2m
, 60%;
Ph
2j
H
H
, 43%
Ph
, 89%;
H
3j
H
Ph
, 32%
Ph
, 85%;
2:3c
c = 90:10
c = 96:4
= 86:14
2k
2:3
H
2l
2:3
N
C
l
C
H
Ph
H
H
Ph
2p
, 58%;
Ph
H
= 91:9
H
Ph
2n
2:3c
2o
2:3c
2:3c
, 78%;
= 92:8
, 48%;
= 90:10
aReactions were carried out with alkyne (1.0mmol), NaBPh4 (1.0mmol), HOAc (2.0mmol), and PdCl2(PPh3)2 (0.03mmol) in a mixture of PEG-400
(1mL) and H2O (1mL) in a sealed tube at room temperature under Ar for 6h.
bIsolated yield.
cDetermined by GC.
Table 3. Palladium-catalyzed hydrophenylation of alkynes with NaBPh4 (0.33 equiv.) in PEG-400/H2O.a,b
PdCl2(PPh3)2
(3 mol%)
R1
R1
Ph
R
R
H
R1
+
NaBPh4
+
R
PEG-400/H2O (1:1)
HOAc (2.0 equiv)
50 oC, 12 h
(0.33 equiv)
Ph
H
1
2
3
n-Bu
n-Bu
n-C5H11
CO2Et
H
Ph
Ph
Ph
H
Ph
CO2Et
CO2Me
MeO2C
Ph
2a
Ph
2d
Ph
H
, 82%
H
Ph
H
2i
, 90%;
2:3c
, 83%;
c = 93:7
2e
, 79%
, 91%
> 99
2h
2:3
n-C6H13
Ph
H
H
Ph
H
H
H
Ph
, 39%;
Ph
Ph
2l
, 54%;
H
:
2:3c
2m
2:3c
2n
2:3c
= 84:16
, 44%;
= 91 9
= 92:8
aReactions were carried out with alkyne (1.0mmol), NaBPh4 (0.33mmol), HOAc (2.0mmol), and PdCl2(PPh3)2 (0.03mmol) in a mixture of PEG-400
(1mL) and H2O (1mL) in a sealed tube at 50°C under Ar for 12h.
bIsolated yield.
cDetermined by GC.
PdCl2(PPh3)2/PEG-400/H2O system was then subjected to a without addition of PdCl2(PPh3)2. In addition, the leaching
second run of the reaction by charging with the same start- of palladium in the product was also determined, and induc-
ing materials (1,2-diphenylacetylene, NaBPh4, and HOAc) tively coupled plasma (ICP) analysis of the crude petroleum

Liu et al.
5
R1
H
PdCl2(PPh3)2
(3 mol%)
R1
Ar
R
R
H
R1
A.rB(OH)2
(1.0 equiv)
3
+
+
R
PEG-400/H2O (1:1)
Ar
c
HOA (2.0 equiv), r.t., 6 h
4
1
5
R, R1 = CO2Me
Ar = 4-MePh
4a:
4b:
4c:
55%
62%;
58%;
R = Me, R1 = CO2Et Ar = 4-MePh
4:5
4:5
> 99
> 99
R = Me, R1 = CO2Et Ar = 4-MeOPh
Scheme 1. Palladium-catalyzed hydroarylation reaction of alkynes with arylboronic acids in PEG-400/H2O (1:1).
were recorded on a Bruker Avance 400 (400MHz) spec-
trometer with tetramethylsilane (TMS) as an internal stand-
ard using CDCl3 as the solvent. 13C NMR spectra were
recorded on a Bruker Avance 400 (100MHz) spectrometer
using CDCl3 as the solvent. HRMS spectra were recorded
on a quadrupole–time of flight Bruker MicroTOF-Q II
mass spectrometer equipped with an electrospray ioniza-
tion (ESI) and atmospheric pressure chemical ionization
(APCI) source. Palladium content was determined with
inductively coupled plasma atom emission Atomscan16
(ICP-AES, TJA Corporation).
R
L2PdCl2
R1
Ph
Ph2B Ph
d
H
L2P (0)
2
L = PPh3
R
Ph
Pd(II)
R1
Ph2B
Ph
C
(
)
A
( )
H
L
L
Pd(II)
L
L
R
R1
R1
R
Ph B
H
O
Ph
2
1
General procedure for palladium-catalyzed
hydrophenylation of alkynes with NaBPh4 in
PEG-400/H2O (1:1)
Ph2B
Pd(II)
H
2O
L
L
B
(
)
A mixture of alkyne 1 (1.0mmol), NaBPh4 (1.0mmol),
HOAc (2.0mmol), PdCl2(PPh3)2 (0.03mmol), PEG-400
(1.0mL), and H2O (1.0mL) was stirred under Ar in a sealed
tube at room temperature for 6h. After completion of the
reaction, the reaction mixture was extracted three times
with petroleum ether (3×10mL). The combined ether
phase was concentrated under reduced pressure, and the
residue was purified by flash column chromatography on
silica gel (eluting with petroleum ether) to afford the desired
product 2.
Scheme 2. Proposed catalytic cycle.
ether extract after the first cycle showed that palladium con-
tent was less than 0.80ppm.
In conclusion, an efficient and recyclable catalytic sys-
tem for the palladium-catalyzed hydrophenylation reaction
of alkynes with sodium tetraphenylborate has been devel-
oped. In the presence of 3mol% PdCl2(PPh3)2 and HOAc,
the hydrophenylation reaction of a variety of alkynes with
NaBPh4 proceeded smoothly at room temperature in PEG-
400/H2O (1:1) to afford the corresponding phenyl-substi-
tuted alkenes in moderate to high yields. Furthermore, the
PdCl2(PPh3)2/PEG-400/H2O system could be recycled up
to six times without apparent loss of catalytic activity. The
present protocol will serve as an efficient and green way to
prepare a variety of phenyl-substituted alkenes. Currently,
further efforts to extend the application of the system in
other palladium-catalyzed organic transformations are
underway in our laboratory.
The residue (the aqueous layer) of the extraction was
heated to 60°C in vacuum for 20min to remove the residual
petroleum ether, and then subjected to a second run of the
reaction by charging with the same starting materials
(alkyne, NaBPh4, and HOAc) without addition of
PdCl2(PPh3)2 under identical conditions. After the first
reaction cycle, the crude petroleum ether extract was sub-
jected to ICP-AES analysis before any further purification.
1
1,1,2-Triphenylethene (2a): Pale yellow oil. H NMR
(400MHz, CDCl3): δ=7.36-6.90 (m, 16H); 13C NMR
(100MHz, CDCl3): δ=143.5, 142.7, 140.4, 137.5, 130.5,
129.6, 128.7, 128.3, 128.2, 127.7, 127.5, 127.4, 126.8,
126.6.33
Experimental
1
(E)-3-phenylhex-3-ene (2b): Pale yellow oil. H NMR
All reagents were purchased from different commercial (400MHz, CDCl3): δ=7.37-7.16 (m, 5H), 5.64 (t, J=7.2Hz,
sources and used as received without further purification 1H), 2.51 (q, J=7.4Hz, 2H), 2.22-2.18 (m, 2H), 1.06 (t,
unless otherwise indicated. All reactions were carried out J=7.4Hz, 3H), 0.99 (t, J=7.6Hz, 3H); 13C NMR (100MHz,
under Ar in a sealed reaction tube with magnetic stirring CDCl3): δ=143.2, 141.1, 130.1, 128.2, 126.5, 126.3, 22.8,
1
and the solvents needed to be de-gassed. H NMR spectra 21.8, 14.4, 13.8.33

6
Journal of Chemical Research 00(0)
Table 4. Recyclability of PdCl2(PPh3)2/PEG-400/H2O system.a
PdCl2(PPh3)2
(3 mol%)
Ph
H
Ph
Ph
+
Ph
Ph
NaBPh4
PEG-400/H2O (1:1)
HOAc (2.0 equiv), r.t.
(1.0 equiv)
1a
2a
Cycle
Time (h)
Yield (%)b
Cycle
Time (h)
Yield (%)b
1
2
3
6
6
6
94
93
94
4
5
6
6
7
8
93
92
91
aReaction conditions: 1a (1mmol), NaBPh4 (1mmol), PdCl2(PPh3)2 (3mol%), HOAc (2mmol), and PEG-400/H2O (1:1, 2.0mL) at room temperature
under Ar.
bIsolated yield.
1
(E)-4-phenyloct-4-ene (2c): Pale yellow oil. H NMR NMR (100MHz, CDCl3): δ=144.2, 138.5, 137.7, 129.3,
(400MHz, CDCl3): δ=7.36-7.18 (m, 5H), 5.66 (t, J=7.2Hz, 128.6, 128.3, 127.7, 127.3, 126.7, 126.2, 17.6.33
1H), 2.48 (t, J=7.6Hz, 2H), 2.19-2.15 (m, 2H), 1.49-1.44
1,1-Diphenylpropene (3j): Colorless oil. 1H NMR
(m, 2H), 1.38-1.33 (m, 2H), 0.97 (t, J=7.4Hz, 3H), 0.88 (t, (400MHz, CDCl3): δ=7.39-7.16 (m, 10H), 6.17 (q,
J=7.2Hz, 3H); 13C NMR (100MHz, CDCl3): δ=143.7, J=7.2Hz, 1H), 1.75 (d, J=7.2Hz, 3H); 13C NMR
140.1, 129.3, 128.2, 126.4, 31.8, 30.8, 23.2, 21.9, 14.1.33
(100MHz, CDCl3): δ=143.1, 142.7, 140.2, 130.3, 128.3,
(E)-5-phenyldec-5-ene (2d): Pale yellow oil. H NMR 128.2, 127.4, 127.1, 126.8, 124.4, 15.8.33
1
(400MHz, CDCl3): δ=7.34-7.18 (m, 5H), 5.64 (t,
2-Phenyl-1-hexene (2k): Pale yellow oil. 1H NMR
J=7.2Hz, 1H), 2.49 (t, J=6.8Hz, 2H), 2.22-2.18 (m, 2H), (400MHz, CDCl3): δ=7.46-7.28 (m, 5H), 5.30 (s, 1H),
1.43-1.26 (m, 8H), 0.93 (t, J=7.0Hz, 3H), 0.87 (t, 5.09 (d, J=1.2Hz, 1H), 2.54 (t, J=7.4Hz, 2H), 1.50-1.36
J=6.6Hz, 3H); 13C NMR (100MHz, CDCl3): δ=143.6, (m, 4H), 0.94 (t, J=7.2Hz, 3H); 13C NMR (100MHz,
140.1, 129.1, 128.1, 126.3, 114.8, 32.1, 31.0, 29.5, 28.3, CDCl3): δ=148.9, 141.6, 128.2, 127.2, 126.1, 112.0, 35.1,
22.7, 22.5, 14.1, 14.0.33
30.5, 22.4, 13.9.48
(Z)-dimethyl 2-phenylmaleate (2e): Yellow oil. 1H NMR
2-Phenyl-1-octene (2l): Pale yellow oil. 1H NMR
(400MHz, CDCl3): δ=7.51-7.37 (m, 5H), 6.31 (s, 1H), (400MHz, CDCl3): δ=7.40-7.23 (m, 5H), 5.25 (s, 1H),
3.94 (s, 3H), 3.78 (s, 3H); 13C NMR (100MHz, CDCl3): 5.04 (s, 1H), 2.49 (t, J=7.2Hz, 2H), 1.46-1.27 (m, 8H),
δ=168.3, 165.4, 149.0, 133.2, 130.6, 129.0, 126.8, 117.1, 0.85 (t, J=6.6Hz, 3H); 13C NMR (100MHz, CDCl3):
52.7, 52.0.33
δ=148.8, 141.6, 128.2, 127.2, 126.1, 112.0, 35.4, 31.7,
(E)-methyl 3-phenylbut-2-enoate (2f): Pale yellow oil. 29.0, 28.3, 22.6, 14.1.33
1H NMR (400MHz, CDCl3): δ=7.49-7.34 (m, 5H), 6.14
1,1-Diphenylethene (2m): Brown oil. 1H NMR
(q, J=1.4Hz, 1H), 3.76 (s, 3H), 2.59 (d, J=1.4Hz, 3H); 13C (400MHz, CDCl3): δ=7.34-7.23 (m, 10H), 5.46 (s, 2H);
NMR (100MHz, CDCl3): δ=167.4, 155.9, 142.2, 129.1, 13C NMR (100MHz, CDCl3): δ=150.2, 141.6, 128.3,
128.6, 126.3, 116.8, 51.2, 18.1.33
128.2, 127.7, 114.2.33
(E)-ethyl 3-phenylbut-2-enoate (2g): Pale yellow oil. 1H
2,5-Diphenyl-1-pentene (2n): Yellow oil. 1H NMR
NMR (400MHz, CDCl3): δ=7.48-7.26 (m, 5H), 6.13 (s, (400MHz, CDCl3): δ=7.38-7.13 (m, 10H), 5.28 (s, 1H),
1H), 4.22 (q, J=7.2Hz, 2H), 2.57 (s, 3H), 1.31 (t, J=7.2Hz, 5.07 (s, 1H), 2.64 (t, J=7.0Hz, 2H), 2.54 (t, J=7.2Hz, 2H),
3H); 13C NMR (100MHz, CDCl3): δ=166.8, 155.4, 142.3, 1.79-1.74 (m, 2H); 13C NMR (100MHz, CDCl3): δ=148.4,
128.9, 128.5, 126.3, 117.3, 59.8, 17.9, 14.3. HRMS calcd 142.3, 141.4, 128.5, 128.3, 127.3, 126.2, 125.7, 112.4, 35.5,
+
for C12H14O2+ [M+]: 190.0994; found: 190.0988.
34.9, 29.9. HRMS calcd for C17H18 [M+]: 222.1409;
(E)-ethyl 3-phenyloct-2-enoate (2h): Pale yellow oil. 1H found: 222.1414.
NMR (400MHz, CDCl3): δ=7.45-7.32 (m, 5H), 6.01 (s,
5-Chloro-2-phenyl-1-pentene (2o): Yellow oil. 1H NMR
1H), 4.21 (q, J=7.2Hz, 2H), 3.09 (t, J=7.6Hz, 2H), 1.45- (400MHz, CDCl3): δ=7.43-7.25 (m, 5H), 5.33 (d,
1.26 (m, 9H), 0.85 (t, J=6.8Hz, 3H); 13C NMR (100MHz, J=1.4Hz, 1H), 5.11 (d, J=1.4Hz, 1H), 3.54 (t, J=6.4Hz,
CDCl3): δ=166.5, 160.8, 141.6, 128.7, 128.5, 126.7, 117.3, 2H), 2.68 (t, J=7.4Hz, 2H), 1.96-1.87 (m, 2H); 13C NMR
59.8, 31.9, 31.0, 28.7, 22.4, 14.3, 14.0.33
(100MHz, CDCl3): δ=146.9, 140.7, 128.4, 127.5, 126.1,
Ethyl 3,3-diphenylacrylate (2i): Pale yellow oil. 1H 113.3, 44.4, 32.4, 31.0.48
NMR (400MHz, CDCl3): δ=7.42-7.21 (m, 10H), 6.39 (s,
5-Cyano-2-phenyl-1-pentene (2p): Yellow oil. 1H NMR
1H), 4.08 (q, J=7.2Hz, 2H), 1.13 (t, J=7.2Hz, 3H); 13C (400MHz, CDCl3): δ=7.42-7.28 (m, 5H), 5.38 (s, 1H),
NMR (100MHz, CDCl3): δ=166.1, 156.5, 140.8, 129.4, 5.16 (s, 1H), 2.72 (t, J=7.2Hz, 2H), 2.35 (t, J=7.2Hz, 2H),
129.1, 128.5, 128.4, 128.3, 127.9, 117.5, 60.1, 14.0.33
1.86-1.79 (m, 2H); 13C NMR (100MHz, CDCl3): δ=146.2,
(E)-1,2-diphenylpropene (2j): White solid; m.p. 81– 140.2, 128.5, 127.8, 126.1, 119.4, 114.0, 34.0, 23.8, 16.4.
82°C. 1H NMR (400MHz, CDCl3): δ=7.53 (d, J=7.2Hz, HRMS calcd for C12H13N+ [M+]: 171.1048; found:
2H), 7.39-7.22 (m, 8H), 6.84 (s, 1H), 2.28 (s, 3H); 13C 171.1046.

Liu et al.
7
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General procedure for palladium-catalyzed
hydroarylation of alkynes with ArB(OH)2 in
PEG-400/H2O (1:1)
A mixture of alkyne 1 (1.0mmol), ArB(OH)2 3 (1.0mmol),
HOAc (2.0mmol), PdCl2(PPh3)2 (0.03mmol), PEG-400
(1.0mL), and H2O (1.0mL) was stirred under Ar in a sealed
tube at room temperature for 6h. After the reaction, the
mixture was extracted three times with petroleum ether
(3×10mL). The combined ether phase was concentrated
under reduced pressure, and the residue was purified by
flash column chromatography on silica gel (eluting with
petroleum ether) to afford the target product 4.
(Z)-dimethyl 2-p-tolylmaleate (4a): Yellow oil. 1H NMR
(400MHz, CDCl3): δ=7.39 (d, J=8.4Hz, 2H), 7.22 (d,
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(s, 3H); 13C NMR (100MHz, CDCl3): δ=168.5, 165.6,
18. Nevado C and Echavarren AM. Synthesis 2005: 167.
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149.0, 141.2, 130.4, 129.8, 126.7, 115.9, 52.7, 52.0, 21.4.
+
HRMS calcd for C13H14O4 [M+]: 234.0892; found:
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234.0887.
(E)-ethyl 3-p-tolylbut-2-enoate (4b): Pale yellow oil. 1H
NMR (400MHz, CDCl3): δ=7.38 (d, J=8.0Hz, 2H), 7.17
(d, J=7.6Hz, 2H), 6.13 (s, 1H), 4.20 (q, J=7.2Hz, 2H),
2.56 (s, 3H), 2.36 (s, 3H), 1.31 (t, J=7.2Hz, 3H); 13C NMR
(100MHz, CDCl3): δ=166.6, 153.9, 139.1, 137.7, 128.4,
126.4, 118.2, 51.9, 21.3, 18.2, 14.4. HRMS calcd for
C13H16O2+ [M+]: 204.1150; found: 204.1152.
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(E)-ethyl 3-(4-methoxyphenyl)but-2-enoate (4c): Pale
yellow oil. 1H NMR (400MHz, CDCl3): δ=7.45 (d,
J=8.8Hz, 2H), 6.89 (d, J=8.8Hz, 2H), 6.11 (s, 1H), 4.20
(q, J=6.8Hz, 2H), 3.83 (s, 3H), 2.56 (s, 3H), 1.31 (t,
J=6.8Hz, 3H); 13C NMR (100MHz, CDCl3): δ=167.1,
160.4, 154.9, 134.4, 127.7, 115.4, 113.9, 59.7, 55.4, 17.7,
+
14.4. HRMS calcd for C13H16O3 [M+]: 220.1099; found:
220.1096.
31. Shintani R, Tsurusaki A, Okamoto K, et al. Angew Chem Int
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Declaration of conflicting interests
32. Cho CS, Motofusa S-I, Ohe K, et al. J Org Chem 1995; 60:
883.
33. Zeng H and Hua R. J Org Chem 2008; 73: 558.
34. Chen J, Spear SK, Huddleston JG, et al. Green Chem 2005;
7: 64.
35. Candeias NR, Branco LC, Gois PMP, et al. Chem Rev 2009;
109: 2703.
36. Turgis R, Billault I, Acherar S, et al. Green Chem 2013; 15:
1016.
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
The author(s) disclosed receipt of the following financial support
for the research, authorship, and/or publication of this article: This
study was financially supported by the National Natural Science
Foundation of China (no. 21462021) and the Natural Science
Foundation of Jiangxi Province of China (no. 20161BAB203086).
37. Hallett JP and Welton T. Chem Rev 2011; 111: 3508.
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ORCID iD
39. Li J-H, Liu W-J and Xie Y-X. J Org Chem 2005; 70: 5409.
40. Liu L, Zhang Y and Wang Y. J Org Chem 2005; 70: 6122.
41. Han W, Liu C and Jin Z-L. Org Lett 2007; 9: 4005.
42. Wang L, Zhang Y, Liu L, et al. J Org Chem 2006; 71: 1284.
43. Ackermann L and Vicente R. Org Lett 2009; 11: 4922.
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2515.
Mingzhong Cai
https://orcid.org/0000-0002-1056-2846
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